This invention relates generally to apparatus for measuring the output power of a prime mover and is particularly directed to a modular dynamometer capable of measuring prime mover output power over a wide range of values.
A dynamometer is a device for measuring the output power of a prime mover. The measurement may be made in terms of the RPMs of a rotating shaft, the torque, or other form of the prime mover's output power. The prime mover of interest may take on the form of virtually any power generating device such as an electric motor, a gasoline or diesel engine, a gas turbine, etc.
A dynamometer may take on various forms including that of a hydraulic brake which makes use of frictional energy conversion to measure prime mover output power. Such hydrokinetic dynamometers generally make use of one or more impellers positioned within a housing containing a working fluid as well as a circulating coolant. Each of the impellers, or rotors, is typically shrink-mounted on a rotating shaft in a spaced manner along the length of the shaft. Disposed between adjacent rotors is one of a plurality of stators. This type of dynamometer is expensive, cumbersome, and of generally fixed configuration, affording a limited output power measuring range. Moreover, such fixed configuration dynamometers are highly susceptible to excessive wear due primarily to cavitation where those components subject to this type of damage are generally inaccessible and thus not replaceable. In addition, the average prime mover repair shop is not capable of servicing such an assembly.
The typical prime mover rebuild/repair facility handles engines, motors, etc., having a wide range of sizes. Horsepower ranges of from 20-100 and from 200-700 up to 3000 horsepower in a single facility are common. Two or more dynamometers are commonly employed to cover this wide output power range. In an effort to reduce expenses a single dynamometer may be employed over a very wide output power range. Torque capacity is calculated as a function of RPM squared, where typical values encountered in the field are given by the following table.
TABLE ______________________________________ RPM TORQUE HORSEPOWER (H.P.) ______________________________________ 2100 5000 2000 1050 1250 250 ______________________________________
Many engine dynamometer operators are forced to purchase a 2000 H.P. rated dynamometer in order to perform a 250 H.P. test of an engine at 1250 RPM. This type of measurement is virtually impossible on many single-rated capacity dynamometers.
Increased output power testing ranges are necessitated by current engine design trends which are to lower RPM's and associated higher torque values. All new diesel truck engines carry a specification labeled "Percent of Torque Rise". Lower engine operating RPM's are also related to:
1. 55 mile per hour speeds; PA1 2. fuel economy; PA1 3. emission standards (particularly the 1991-94 requirements); PA1 4. longer engine life; PA1 5. extended manufacturer's warranties; and PA1 6. reduced engine weights with same horsepower rating.
One approach to increasing the measurement range of a hydrokinetic dynamometer involves the replacement of various components of he dynamometer, including the rotors, with different sized components. While offering an increased power measurement range, this approach relies upon a number of common components having different dimensions including size and weight variations, and thus is rather expensive and of limited commercial appeal. In addition, the use of limited production quantities of many different sized parts which are non-interchangeable is very uneconomical in terms of manufacturing costs. There is thus a great demand and need for expandable test equipment.
The present invention overcomes the aforementioned limitations of the prior art by providing a modular dynamometer which makes use of a basic rotor/stator module which may be used either by itself or with virtually any number of such modules to afford a wide output power measuring range. This invention eliminates the requirement of investing in, housing and maintaining large dollar amounts of surplus test facilities. The rotor is easily attached to or removed from a rotating shaft coupled to the prime mover, while each of the stators is easily installed in or removed from the dynamometer housing which is of fixed size and is easily assembled and disassembled. By making use of uniform modules all having the same configuration and dimensions, the present dynamometer offers an inexpensive approach for a dynamometer capable of accommodating a wide range of output power.